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xen: Speed up set_phys_to_machine() by using read-only mappings 

Instead of checking at each call of set_phys_to_machine() whether a
new p2m page has to be allocated due to writing an entry in a large
invalid or identity area, just map those areas read only and react
to a page fault on write by allocating the new page.

This change will make the common path with no allocation much
faster as it only requires a single write of the new mfn instead
of walking the address translation tables and checking for the
special cases.

Suggested-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
This commit is contained in:
Juergen Gross 2014-11-28 11:53:59 +01:00 committed by David Vrabel
parent 054954eb05
commit 2e917175e1
1 changed files with 8 additions and 6 deletions
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14
arch/x86/xen/p2m.c
View File

@ -70,6 +70,7 @@
#include <asm/cache.h>
#include <asm/setup.h>
#include <asm/uaccess.h>
#include <asm/xen/page.h>
#include <asm/xen/hypercall.h>
@ -316,9 +317,9 @@ static void __init xen_rebuild_p2m_list(unsigned long *p2m)
paravirt_alloc_pte(&init_mm, __pa(p2m_identity_pte) >> PAGE_SHIFT);
for (i = 0; i < PTRS_PER_PTE; i++) {
set_pte(p2m_missing_pte + i,
pfn_pte(PFN_DOWN(__pa(p2m_missing)), PAGE_KERNEL));
pfn_pte(PFN_DOWN(__pa(p2m_missing)), PAGE_KERNEL_RO));
set_pte(p2m_identity_pte + i,
pfn_pte(PFN_DOWN(__pa(p2m_identity)), PAGE_KERNEL));
pfn_pte(PFN_DOWN(__pa(p2m_identity)), PAGE_KERNEL_RO));
}
for (pfn = 0; pfn < xen_max_p2m_pfn; pfn += chunk) {
@ -365,7 +366,7 @@ static void __init xen_rebuild_p2m_list(unsigned long *p2m)
p2m_missing : p2m_identity;
ptep = populate_extra_pte((unsigned long)(p2m + pfn));
set_pte(ptep,
pfn_pte(PFN_DOWN(__pa(mfns)), PAGE_KERNEL));
pfn_pte(PFN_DOWN(__pa(mfns)), PAGE_KERNEL_RO));
continue;
}
@ -624,6 +625,9 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn)
return true;
}
if (likely(!__put_user(mfn, xen_p2m_addr + pfn)))
return true;
ptep = lookup_address((unsigned long)(xen_p2m_addr + pfn), &level);
BUG_ON(!ptep || level != PG_LEVEL_4K);
@ -633,9 +637,7 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn)
if (pte_pfn(*ptep) == PFN_DOWN(__pa(p2m_identity)))
return mfn == IDENTITY_FRAME(pfn);
xen_p2m_addr[pfn] = mfn;
return true;
return false;
}
bool set_phys_to_machine(unsigned long pfn, unsigned long mfn)